It’s a home made setup that was already in the van when I bought it, the previous owner was an outdoorist too.
There are two removable boards across the van for the front section, which over lap the folded middle seat to give a good length bed. These can form a handy ‘shelf’ behind the middle seat or be stored vertically behind the seat (as shown) to give full load space. The rear end of the bed is two fold up sections attached to framework/storage built in. The whole lot is ply topped with foam and then carpet, firm but quite comfortable really. Two bikes comfortably fit under the bed with front wheels off.
There are also a second set of floor mounts for the middle seat set back from the normal ones, too close to add a third row, but that puts the seat under the bed out of the way. Or when only the rear boards are down and the seat up it gives a nice spacious seating area, front seats on swivels.